Non-volatile memories (NVMs) have been used as auxiliary storage devices or storages in recent information processing systems. Non-volatile memories are broadly divided into flash memories for data access in units of large data sizes and non-volatile random access memories (Non-volatile RAMs) to which high-speed random access is possible in units of smaller data sizes. Here, NAND flash memories are exemplified as a representative example of flash memories. On the other hand, resistive RAMs (ReRAMs), phase-change RAMs (PCRAMs), magnetoresistive RAMs (MRAMs), and the like are exemplified as examples of non-volatile random access flash memories. Among these memories, ReRAMs have attracted attention due to high access speed and the like.
Generally, in ReRAMs, a memory cell including a variable resistive element is disposed at each of intersection points of column lines and row lines which are wired in a two-dimensional lattice pattern. A driver selects a memory cell of a rewrite target on the basis of write data and applies a voltage between the column line and the row line to cause a resistance value of the selected memory cell to be changed. If a leakage current occurs in an unselected memory cell, the leakage current flows into the selected memory cell via the column line or the row line, and a voltage drop (IR drop) equal to a product of the leakage current and a wiring resistance of the row line or the column line occurs. As the IR drop increases, a writing time to the memory cell increases. Further, if the IR drop differs for each memory cell, there occurs a variation in the writing time of each memory cell. Further, in a case in which a certain margin is given to a power supply voltage so that a value after the drop does not fall below a certain minimum operation voltage even when the power supply voltage drops due to the IR drop, the margin decreases as the variation of the IR drop increases.
In this regard, a memory controller that performs rewriting to a high resistance state in order from a memory cell in which a wiring distance of the row line or the column line is small in a write process in order to suppress a fluctuation of the IR drop has been proposed (see, for example, Patent Literature 1). As the resistance value of the memory cell increases, the leakage current decreases, and as the wiring distance increases, the wiring resistance increases, and thus it is possible to suppress the variation of the IR drop to some extent by rewriting to the high resistance state in order from the memory cell having the small wiring distance.